The invention is related to a floating-caliper spot-type disc brake having brake shoes which are actively restored after the operation of the brake, a constant clearance being adjusted independently of the wear of the friction lining.
In a spot-type disc brake of this type shown in German patent specification No. 35 10 372, a floating caliper is axially slidingly guided on a brake carrier by means of pin guides. The floating caliper is furnished with a hydraulic actuator comprising a brake cylinder and a brake piston actuated to cause an axially internal brake shoe to be urged against the brake disc. A reaction force slides the brake caliper to urge an external brake shoe against the brake disc.
The brake shoes are actively restored after the actuation to ensure a constant clearance between the friction areas and the brake disc not withstanding wear of the brake linings. In this context, the directly actuated brake shoe is restored in the known manner by the brake piston which is retracted by a special sealing between the piston wall and the brake cylinder, which then entrains the abutted brake shoe. The whole brake caliper must be slid back in order to restore the brake shoe.
In a disc brake which is known from the German patent specification No. 35 10 372, this takes place due to a special pin guide which is comprised of a ring being frictionally engaged by the pin and of a cup spring engaging the ring and a retaining member on the floating caliper. Upon actuation of the brake, sliding of the floating caliper causes tensioning of the cup spring After the actuation of the brake, the cup spring pushes the floating caliper back. With advancing wear of the lining, the actuating travel of the brake caliper becomes longer than the clearance to be adjusted so that the cup spring, upon reaching a stop, forces the friction ring to slide a little farther on the pin. In this manner it is insured that the floating caliper is subsequently restored not more than the desired clearance.
This prior-art arrangement disadvantageously is comprised of many components having a complicated shape whose manufacture and mounting incur comparatively high costs. It is a further disadvantage that the pin guides are disposed on the axially internal side and the brake shoe to be cleared is disposed on the axially external side of the floating caliper. In the event of a high force braking, the floating caliper will be elastically stretched so that the actuating travel which occurs at the pin guides will be greater than that at the external brake shoe. This results in a shifting of the friction ring without a corresponding wear of the lining having occurred, with the consequence that in an extreme case no clearance will be adjusted at all and the brake shoe will constantly forced against the brake disc.
It is the object of the invention to provide a spot-type disc brake which is equipped with simple adjustment arrangement for the external brake shoe.